Mixers for viscous liquids and masses are known in manifold embodiments. They usually work with stirring or kneading tools which rotate within a housing and might perform a planetary motion in addition to the rotary motion about their own axis. For example DE-C 439 990, from which the invention departs, describes an apparatus for refining chocolate or similar plastic masses wherein mixer shafts in the form of rolls are disposed within a cylindrical housing so as to revolve about a center roll and simultaneously rotate about their own axes in the same direction, all or individual rolls--possibly including the center roll--having openings such that the material to be processed is able to penetrate them perpendicular to their longitudinal axis. The roll openings can be twisted helically, the result being that the material to be processed undergoes not only a motion perpendicular to the roll axis but also one in the longitudinal direction of the rolls. This device requires comparatively complicated mixing tools and is not readily suitable for processing viscous liquids for example. Furthermore it is difficult to clean, and mainly limited to its special purpose, namely the refining of chocolate masses.
In addition there are so-called thin-layer reactors (compare for example DE-C 30 30 541) which likewise work with shafts disposed in a ring within a cylindrical housing. The shafts bear meshing, in particular disk-shaped treating members for the material to be processed which limit thin gaps with each other through which the material is conveyed while being simultaneously spread in a thin layer. The material to be,processed is brought from a thick-layer side onto a thin-layer side where a vacuum may be effective to cause degassing of the material spread in a thin layer.
With such thin-layer reactors one strives for a comparatively long sojourn time of the material to be processed in the reactor. Although they permit viscous media, for example molten polymer masses or the like, to be mixed with additives they are neither intended nor suitable for use strictly as mixers for viscous liquids or masses.